1. Field of the Invention
Embodiments relate to a light diffusion film with uniform surface roughness and a low retardation value, a display including the same, and associated methods.
2. Description of the Related Art
Light diffusion films refer to a variety of products used to uniformly distribute light and maintain overall light transmission while hiding defects which may occur during light guiding. Such light diffusion films may be used in liquid crystal display devices, e.g., car navigations, mobile phones, PDAs, digital cameras, portable TVs, camcorders, small or large sized notebook PCs, monitors for desktop PCs, and the like.
At present, a great deal of research in the field of light diffusion films for liquid crystal display backlight units has focused on developing a light diffusion film capable of uniformly diffusing light without any light loss, when the light emitted from a light source passes through a diffusion layer of the film.
Conventional light diffusion films must overcome various problems. These problems may include lack of dimensional stability, coating defects caused by lack of durability in coating process, scratch defects in a coating layer, non-uniformity of surface texture, dust adhesion derived from electrostatic generation, and reduced brightness or brightness non-uniformity caused by the above defects.
In order to solve the above problems, it is desirable to impart light diffusion performance to a diffusion layer of a light diffusion film without using a diffusing agent or a coating process, and to improve the uniformity of light transmission and diffusion of the same.
In an effort to ensure uniformity of light transmission and diffusion, research has been conducted into formation of an embossing pattern on a film itself so as to effectively scatter and transmit irregular light from a light source, resulting in uniform brightness. However, due to unevenness of the formed embossing patterns, the above approach has problems achieving uniform light transmission and light diffusion. In addition, conventional light diffusion films are evaluated only by their roughness (Ra) values, thus making it difficult to uniformly control surface roughness without deviation.
Another approach to improving the brightness of liquid crystal display devices is to reduce retardation of light transmission films of backlight units. When optical distortion remains inside the light diffusion film during the production process, the retardation value of the film is increased, which is a main cause of brightness deterioration. One method of imparting a low retardation value to the film is to maintain a resin cooling roll of an extrusion device at a temperature not less than the glass transition temperature (Tg) of the resin. However, this may inhibit the surface of the film from maintaining its embossing pattern, thus causing a lower haze value. Loosely holding the film between a cooling roll and a transport roll may also be effective. This method, however, may exert only a slight reduction in retardation.